p0420 code help! with freeze frame data

[gio89]

I have a 2002 toyota solara 4 cylinder
I recently got a p0420 mil light on my car. The car has no problems running, no difference at all actually and the light turns off by itself. It has came on and off twice and is still off.
After doing some research i heard it might be because the o2 sensors have never been changed since the life of the car. The car has 180,000 miles.
The reason i am asking if its the o2 sensors, even though the light is now off is because the gas mileage has gotten real bad.
here is the information:
P0420 (catalyst system efficiency below threshold (bank 1))
Freeze frame data
fuel sys 1...................CL
fuel sys 2...................NA
calc load (%)..............55.29
ECT(degreesC).............85
STFT B1 (%)................1.56
LTFT B1 (%)................3.91
Eng RPM....................2110
veh speed (km/h)..........54
IAT(degreesC)..............30

[SteveSolara]

EGR Valve??? Maybe clean that out it prob helps or take the bank1 O2 sensor off clean it and let it dry than plug it back in and take off the negative battery terminal for 30 sec and plug it back in. Hopefully it was just dirty, but 180K miles i'd rather change it, but they are pretty pricy

[gio89]

Ok, i ended up paying for a new front o2 sensor and turned the check engine light off, and so far it has been good. And the gas mileage has been much better. but today the light came back on with the same code, but a very different readout. Here is the new information...
P0420 (catalyst system efficiency below threshold (bank 1))
Freeze frame data
fuel sys 1...................CL
fuel sys 2...................NA
calc load (%)..............62.75
ECT(degreesC).............82
STFT B1 (%)................-0.78
LTFT B1 (%)................10.94
Eng RPM....................2141
veh speed (km/h)..........91
IAT(degreesC)..............26


If someone could tell me whats going on with my car it would help me out so much.